Rocking chair or insertion secondary batteries are a type of energy storage device in which carrier ions, such as lithium, sodium, potassium, calcium or magnesium ions, move between a positive electrode and a negative electrode through an electrolyte. The secondary battery may comprise a single battery cell, or two more battery cells that have been electrically coupled to form the battery, with each battery cell comprising a positive electrode, a negative electrode, a microporous separator and an electrolyte.
In rocking chair battery cells, both the positive and negative electrodes comprise materials into which a carrier ion inserts and extracts. As a cell is discharged, carrier ions are extracted from the negative electrode and inserted into the positive electrode. As a cell is charged, the reverse process occurs: the carrier ion is extracted from the positive and inserted into the negative electrode.
FIG. 1 shows a cross sectional view of an electrochemical stack of an existing energy storage device, such as a non-aqueous, lithium-ion battery. The electrochemical stack 1 includes a positive electrode current collector 12, on top of which a positive electrode active material layer 13 is assembled. This layer is covered by a microporous separator 14, over which an assembly of a negative electrode current collector 15 and a negative electrode active material layer 16 are placed. This stack is sometimes covered with another separator layer (not shown) above the negative electrode current collector 15, rolled and stuffed into a can, and filled with a non-aqueous electrolyte to assemble a secondary battery.
The positive and negative electrode current collectors pool electric current from the respective active electrochemical electrodes and enable transfer of the current to the environment outside the battery. A portion of a negative electrode current collector is in physical contact with the negative electrode active material while a portion of a positive electrode current collector is in physical contact with the positive electrode active material. The current collectors do not participate in the electrochemical reaction and are therefore restricted to materials that are electrochemically stable in the respective electrochemical potential ranges for the anode and cathode.
To bring current from the current collectors to the environment outside the battery, the negative electrode and positive electrode current collectors are typically each connected to an electrode bus, tab, tag, package feed-through or housing feed-through, typically collectively referred to as contacts. One end of a contact is connected to one or more current collectors while the other end passes through the battery packaging for electrical connection to the environment outside the battery. The negative electrode contact is connected to the negative electrode current collectors and the positive electrode contact is connected to the positive electrode current collectors by welding, crimping, or ultrasonic bonding or is glued in place with an electrically conductive glue.
Conventional wound batteries (see, e.g., U.S. Pat. Nos. 6,090,505 and 6,235,427) typically have electrode materials (active materials, binder, conductivity aid) coated onto a single foil and compressed prior to cell assembly. The foil onto which the electrode is coated onto is typically part of the current collection path. In single jellyroll batteries such as the 18650 or prismatic cells, the current collector foil is ultrasonically welded to electrode buses, tabs, tags etc., that carry the current from the active materials, through the current collector foils and the tabs, to the outside of the battery. Depending on the design, there may be tabs in multiple places along a single jellyroll, or along one place in one or both ends of the current collector foil. Conventional stacked battery pouch cells have multiple plates (or foils) of active material with areas on top of each foil that are subsequently gathered and welded together to a tab; which then carries the current to the outside of the battery pouch (see, e.g., U.S. Patent Publication No. 2005/0008939).
Referring again to FIG. 1, during a charging process, lithium leaves the positive electrode cathode layer 13 and travels through the separator 14 as lithium ions into negative electrode active material layer 16. Depending upon the negative electrode active material used, the lithium ions either intercalate (e.g., sit in a matrix of the negative electrode active material without forming an alloy) or form an alloy. During a discharge process, the lithium leaves negative electrode active material layer 16, travels through the separator 14 and enters positive electrode active material layer 13. The current conductors conduct electrons from the battery contacts (not shown) to the electrodes or vice versa.
Battery separators are used to separate the anode and cathode during assembly and battery operations. Separators for existing lithium ion batteries typically use thin porous insulating materials with high ion permeability, good mechanical stability, and good chemical compatibility to the battery chemistries. Structurally, the separator should have sufficient porosity to absorb liquid electrolyte for the high ionic conductivity. It mostly is a microporous layer consisting of either a polymeric membrane or a non-woven fabric mat.
Existing energy storage devices, such as batteries, fuel cells, and electrochemical capacitors, typically have two-dimensional laminar architectures (e.g., planar or spiral-wound laminates) as illustrated in FIG. 1 with a surface area of each laminate being roughly equal to its geometrical footprint (ignoring porosity and surface roughness).
Three-dimensional batteries have been proposed in the literature as ways to improve battery capacity and active material utilization. It has been proposed that a three-dimensional architecture may be used to provide higher surface area and higher energy as compared to a two dimensional, laminar battery architecture. There is a benefit to making a three-dimensional energy storage device due to the increased amount of energy that may be obtained out of a small geometric area. See, e.g., Rust et al., WO2008/089110 and Long et. al, “Three-Dimensional Battery Architectures,” Chemical Reviews, (2004), 104, 4463-4492.
Despite the advances made to-date, a need remains for secondary batteries and other energy storage devices having increased energy density.